Effector cell lineage commitment in allergic inflammation Project summary: The recruitment and expansion of progenitor cells to the lung may be critical for the maintenance and propagation of chronic airway inflammation in asthma. The origin of the tissue mast cell progenitor remains elusive. The current paradigm describing the origin of the mast cell states that mast cells are derived from hematopoietic (CD45+) bone marrow progenitors, travel though the circulation, and complete their differentiation in diverse target tissues. Preliminary data included in this proposal suggest that 1. a non-hematopoietic progenitor cell (CD45-), previously implicated as a vascular progenitor in vivo, can differentiate into a mast cell, and 2. development of mast cells from CD45- progenitors is increased in asthmatic subjects. This proposal hypothesizes that the mast cell can be derived from a non-hematopoietic, multipotent progenitor whose ultimate lineage commitment is directed by disease-specific microenvironmental factors in asthma. Experiments in Aim 1 seek to define the determinants of CD45- non-hematopoietic progenitor cell differentiation into mast cells. Experiments in this aim propose to identify the cytokine signaling pathways critical for mast cell lineage commitment, test the hypothesis that activation of STAT5 is necessary for mast cell differentiation, and explore mast cell transcriptional networks with emphasis on direct programming of progenitors to mast cells. Experiments propose to test the hypothesis that Th2 cytokines such as IL-4 directly contribute to the multipotent potential of these progenitors by modulating multipotency, self-renewal, and chromatin remodeling genes. Experiments in Aim 2 propose to address the role of mast cells derived from CD45- progenitor cells in human asthma by identifying these progenitors in the peripheral blood of asthmatic vs. normal subjects and identifying CD45- mast cells in human lung pathology specimens, including in those with gender-mismatched lung transplants. The unique functional properties of CD45- mast cells will be studied in organotypic co-culture with human airway epithelial cells derived from normal and asthmatic donors. If successful, these studies will have identified a novel, nonhematopoietic mast cell progenitor, clarified the mechanisms by which these progenitors commit to mast cell development, implicated Th2 cytokines in influencing multipotency gene expression, articulated the role of these cells in human asthma, and proposed new targets for asthma therapeutics.